Food in Relation to Work. 
By Frederic I. Scard, F.C.S. 
T is now forty years ago that GROVE, by the 
enunciation of the great principle of the " cor- 
relation of the natural forces" marked an epoch 
in the advance of science. Prior to that date, the views 
held by scientists with regard to the relative positions of 
the so-called " forces" were vague and unsatisfactory. 
Heat, light, magnetism, electricity, etc., were considered 
to possess distinct features and idiosyncratic properties, 
and more especially what was then termed "vital force'' 
was considered to be independent of, and to possess no 
analogy to the others. The operations of the animal 
system, indeed, were looked upon as admitting of no 
explanation apart from the mysterious influence of life ; 
and it may be said that the views of physiology were 
but slightly advanced since the time when, side by side 
with the transmutation of metals and the philosopher's 
stone, the " elixir of life" formed such a prominent ob- 
ject of research among the philosophers of the middle 
ages. 
GROVE'S doctrine may be briefly summed up in his own 
words, " that any force capable of producing another 
may in its turn be produced by it," or, otherwise ex- 
pressed, that all the different forms of "energy" — heat, 
light, electricity, magnetism, chemical affinity, motion, 
etc., are mutually convertible, any one being capable of 
yielding its equivalent quantity of another, 
